In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date, publicly available, known to the public, part of common general knowledge; or known to be relevant to an attempt to solve any problem with which this specification is concerned.
While the present invention will be described with reference to the production of crayfish, such as yabbies in Australia, the invention is not geographically limited and extends to production of other freshwater or marine organisms including crustacea, exotic fish, shell fish and corals.
Although there is a large commercial market for crayfish in Australia the crayfish aquaculture industry suffers from problems such as inconsistency of catch size and variable yield from one harvest to the next. This in turn means that financial returns to producers are inconsistent and variable.
Despite this, Australia is one of the world's highest producers of yabbies (Cherax destructor and associated species). Primarily these yabbies are produced throughout the southern areas of Australia where the weather conditions suit the yabby very well. However, traditional commercial yabby farming techniques have the disadvantage of propagation of the yabbies. Furthermore, the correct soil type is required to hold the necessary water volumes and the dams must be located within certain geographical areas to facilitate convenient distribution of the yabbies produced.
Yabbies are relatively hardy creatures which proliferate in what the casual observer would consider to be murky, turbid waterways and are generally consistent, self maintaining breeders. However they can be affected by stress. Unfavourable environmental conditions such as overcrowding, limited feed, unfavourable weather conditions and poor water quality can cause stress levels to rise to a point where the yabbies die. This has a severe impact on the harvest yield. Mortality rates of up to 95% of juvenile yabbies, are typical in traditional farming techniques. Juveniles that do survive, and grow to minimum table size of at least 35 grams are often damaged during harvesting, usually when their claws or legs are broken. This further reduces the proportion of marketable yabbies in the harvest.
Harvest yield is also affected by pilfering. Because traditional yabby farming uses large dams which are located in relatively isolated parts of farm paddocks it is difficult to stop birds, eels and fish from preying on the developing yabbies. It is also not uncommon for looters to drag a net through a dam and steal the developing yabbies.
In an effort to increase yabby production, efforts have been made to commercially produce yabbies in large containers that mimic dams. While these large containers can be located at a wider and more convenient range of locations, the problems of avoiding stress must still be addressed. The yabbies in these large containers are stored in a series of rectangular wire cages packed one on top of the other. Accordingly refuse and uneaten food, from the uppermost cages sinks downwards such that the yabbies in the lower cages suffer stress and a high mortality rate.
It has now been found that many of the problems associated with traditional farming techniques can be alleviated, thus providing improved market yields.